In most modern societies, mobile phones are used by people of all ages and walks of life. Once owned and carried by the affluent or persons in specialized occupations that both required and supplied them, mobile phones are now owned by many, and sometimes even by the majority of a given population.
There are many reasons for the widespread use of mobile phones. The first and foremost reason is technology advancements. The development of a cellular system of organizing radio traffic has made it possible to subscribe thousands of customers in a single metropolitan area. Improved multiplexing and modulation techniques have contributed to the ability to handle vast numbers of customers. Coverage has improved as well. That is, the amount of geographic areas serviced by cellular phone companies has increased. At the same time, the cost of mobile phones and subscriptions to a mobile communication network have fallen and made mobile phone use affordable. Improved technology has also led to the development of ever smaller and easier to use phones. These advancements have spurred the mobile phone market, which in turn, fuels more advancement in the mobile phone field.
Some of these improvements, however, present new challenges to mobile phone engineers. The small phone designs of today force developers to economize the size and weight of protective casing components. In other words; to satisfy consumer demands for more portable and lightweight phones, the instruments' ability to absorb shock and resist deformation that might damage internal parts is compromised. In addition, mobile phones are increasingly being used in environments hostile to the sophisticated electronic technology of mobile phones. This is in contrast with the past, when a limited number of rather expensive phones having limited capabilities were mostly used by professionals, and then frequently from a fixed automobile installation. Some prior mobile phones were truly mobile, but were carried about in large protective cases. The small, lightweight, and relatively inexpensive phones of present, however, are owned by customers from all walks of life, and with occupations or avocations that take them and their phones into industrial plants, construction sites, and all manner of outdoor environments. Yet the small, modern phones of present are often less, not more rugged, and at the same time less able to resist hazards like dust and dirt.
Most modern mobile phone enclosures are composed of multiple covers; typically a front cover and a back cover secured to an internal frame. Despite the availability of alternate materials, these covers are often constructed of hard plastic material. In many ways, plastics are well suited as enclosures of portable electronic devices. Plastic (meaning thermoplastic) materials flow when heated to a certain temperature, and can be molded into precise shapes that they retain when cooled. Being non-metallic, plastics are relatively lightweight, non-conducting, and nonmagnetic, which are often favorable properties in connection with portable electronic device enclosures. “Hard” plastic materials resist any deformation at normal operating temperatures (those that human operators will tolerate). Plastics cannot be significantly bent or stretched without application of permanent deformation or failure force. They are strong enough, however, that a substantial force is required to bring such failure about.
One drawback of hard plastic covers is their lack of ability to absorb shock when an abrupt force is applied to the mobile device, such as dropping the device. This type of impact may cause the enclosure to break or may transfer the force to the device's sensitive internal parts. Either outcome generally results in sever damage to the mobile phone. To make up for the enclosure's inability to absorb shock, a separate cover is sometimes used. While separate covers are useful in some ways, they are often under utilized because they hinder the telephone's convenient use and are cumbersome to carry and install.